The present invention relates to the use of a finite element analysis in order to design and/or select orthodontic appliances.
Orthodontics is a branch of dentistry that involves the movement of malpositioned teeth to orthodontically correct positions. Before prescribing an orthodontic treatment, X-rays and photographs of the patient""s teeth and jaw structure are usually taken. Also, a mold of the patient""s teeth is typically made. This mold along with the X-rays and photographs provide a model of the positions of the patient""s teeth and dental arches prior to treatment.
The orthodontist also relies on a post treatment model of the desired positions of the patient""s teeth and dental arches. This post-treatment model has typically been a mental model formulated in the mind of the orthodontist based on the orthodontist""s experience and skill. However, computer programs are also known to assist the orthodontist in the development of a computerized post-treatment model. The orthodontist then devises an initial treatment strategy to move the patient""s teeth and/or dental arches from their positions as represented by the pre-treatment model to the desired positions as represented by the post-treatment model.
In order to implement the initial treatment strategy, the orthodontist applies various orthodontic appliances to the patient""s teeth. In a typical treatment, brackets are attached to anterior, cuspid, bicuspid, and molar teeth. An archwire is then be held to the brackets by ligatures so that the archwire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. The brackets, archwires, ligatures, and other ancillary devices used in correctly positioning teeth are commonly referred to as xe2x80x9cbracesxe2x80x9d.
The orthodontist""s treatment strategy frequently requires correction of the relative alignment between the upper and lower dental arches. For example, certain patients have a condition referred to as a Class II malocclusion in which the lower dental arch is located an excessive distance in a rearward direction relative to the location of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion in which the lower dental arch is located in a forward direction of its desired location relative to the position of the upper dental arch when the jaws are closed.
Orthodontic treatment of Class II and Class III malocclusions are commonly corrected by movement of the upper and lower dental arches as units relative to one another. To this end, forces are often applied to each dental arch as a unit by applying a force to the brackets, the archwires, and/or ancillary devices applied to the dental arch. In this manner, a Class II or Class III malocclusion can be corrected at the same time that the archwires and the brackets are used to move individual teeth to desired positions relative to each other.
Corrections of Class II and Class III malocclusions are sometimes carried out by use of other devices such as headgear that include strapping which extends around the rear of the patient""s head. The strapping is often coupled by tension springs to the brackets, archwires, and/or ancillary devices. For correction of Class III malocclusions, the strapping can be connected by tension springs to a chin cup that externally engages the patient""s chin. In either instance, the strapping and springs serve to apply a rearwardly directed force to the associated jaw.
Instead of using headgear which is often considered unsatisfactory because it is visibly apparent, many practitioners and patients favor the use of intra-oral devices for correcting Class II and Class III malocclusions. Such devices are often located near the cuspid, bicuspid, and molar teeth and away from the patient""s anterior teeth. As a result, intra-oral devices for correcting Class II and Class III malocclusions are hidden in substantial part once installed.
Orthodontic force modules made of an elastomeric material have also been used to treat Class II and Class III malocclusions. Pairs of such force modules are coupled between the dental arches on opposite sides of the oral cavity. Elastomeric force modules may be used in tension to pull the jaws together in a direction along reference lines that extend between the points of attachment of each force module. Such force modules may be O-rings or chain-type modules each made of a number of integrally connected O-rings. These modules are typically removable by the patient for replacement when necessary, since the module may break or the elastomeric material may degrade during use to such an extent that the amount of tension exerted is not sufficient. Non-removable intra-oral devices are also known which rely on flexible members that are connected to upper and lower dental arches of a patient. Moreover, telescoping tube assemblies that may be used to urge the dental arches toward positions of improved alignment are known.
As can be seen, there are a wide variety of orthodontic appliances that are available to an orthodontist in the implementation of a treatment strategy. However, few, if any, tools exist to assist the orthodontist in the accurate selection of appliances that are likely to effectively implement the orthodontist""s initial treatment strategy. Moreover, few, if any, tools exist to allow the orthodontist to accurately predict the effectiveness of the initial treatment strategy. Therefore, the treatment strategy is frequently modified over time as the orthodontist observes the actual movement of the teeth and dental arches in response to the orthodontist""s treatment strategy.
The use of a finite element analysis has been known in the area of orthodontics. For example, U.S. Pat. No. 5,131,844 discloses that a finite element structural model of an individual tooth or a set of teeth may be developed to determine stress distributions under various loading conditions. This patent suggests that such a model may then lead to new approaches to the testing of dental materials, the studying of the effects of bite dislocations, and the determination of proper restorative conditions. This patent further suggests that the model can be used for the design of prosthodontics. U.S. Pat. No. 4,975,052 discloses that a finite element model has been used to determine the optimum angles for a retractor assembly. It is also known to use a finite element analysis to determine how loads applied to brackets generate tensile stresses in the material of the brackets.
However, a finite element analysis has not been used to study the interaction between orthodontic appliances and teeth in order to develop an effective orthodontic treatment strategy.
In accordance with one aspect of the present invention, a method of analyzing an orthodontic treatment comprises the following: modeling first positions of a patient""s teeth; modeling desired second positions of the patient""s teeth; and, performing a finite element analysis based on the orthodontic treatment and a movement of the patient""s teeth between the first and second positions.
In accordance with another aspect of the present invention, a method of determining an effective orthodontic treatment comprises the following: a) creating a first model based upon first positions of a patient""s teeth; b) creating a second model based upon second positions of the patient""s teeth, wherein the second positions represent desired positions of the patient""s teeth; c) selecting a proposed set of orthodontic appliances according to a proposed orthodontic treatment; d) performing a finite element analysis based on the proposed orthodontic treatment and a movement of the patient""s teeth between the first and second positions; e) selecting a new set of orthodontic appliances if the finite element analysis indicates that the proposed orthodontic treatment produces undesired effects; and, f) repeating d) and e) as necessary until the effective orthodontic treatment is achieved.
In accordance with yet another aspect of the present invention, a computer readable storage medium has program code stored thereon which, when executed by a computer, performs the following tasks: a) storing a first position model of a patient""s teeth; b) storing a second position model of the patient""s teeth, wherein the second position model represents desired positions of the patient""s teeth; c) storing a set of orthodontic appliances; d) applying the set of orthodontic appliances to the patient""s teeth according to one of the first and second position models; and, e) performing a finite element analysis based on the first position model, the second position model, and the applied set of orthodontic appliances.
In accordance with still another aspect of the present invention, a method, implemented with the assistance of a computer, of determining an effective orthodontic treatment comprises the following: a) storing first positions of a patient""s teeth; b) displaying the patient""s teeth according to the first positions; c) selecting orthodontic appliances according to a proposed orthodontic treatment of the patient""s teeth; d) storing second positions of the patient""s teeth, wherein the second positions are desired positions; e) installing the selected orthodontic appliances on the patient""s teeth in the second positions; and, f) performing a finite element analysis to assess effects on the orthodontic appliances and on the patient""s teeth based on the first and second positions and on the proposed orthodontic treatment.